99 Blazer: vibration noise at speed

99 blazer, 4.3L, 4wd

I get a vibration or low hum noise with speeds in excess of 50/55 until about 70 mph. It is the worse at 65mph. I recently (3/08) replaced the upper & lower ball joints, pitman/idler arms and right front hub assembly. I just (saturday) purchased 4 new tires due to previous misaligned wear and had a 4wheel alignment. I am still getting the noise/vibration at speed. It does not change with turning, braking or acceleration.

I am concerned it may be the U-joints or 4wd components. I have not tried messing with the 4wd yet. I would appreciate any advice.

Are you sure you are not getting tire noise?
Also check the other wheel bearing real close.
Does noise change under load or coasting?

I agree to check the other wheel bearing real close. Try this, as your driving, around 40 or so, shift the truck into 4wd. Let it engage, and see if the noise/vibration goes away. Get it up to 60 or so and see what you get.

The vibration & sound was present prior to the new tires and alignment and has not changed. I have not checked the driver's wheel hub yet but the sound does not change under load, coasting, even shifting into neutral. I get no vibration thru the steering wheel, it is all general vehicle vibration & noise. I will try the 4wd on the way home tonight. Thanks for the help...

The vibration & sound was present prior to the new tires and alignment and has not changed. I have not checked the driver's wheel hub yet but the sound does not change under load, coasting, even shifting into neutral. I get no vibration thru the steering wheel, it is all general vehicle vibration & noise. I will try the 4wd on the way home tonight. Thanks for the help...

You are welcome.
Tire viveration or shake at 65 points to bad tire/rim bent or wheel balance.
Does noise and vivertion happen at same time and at same speed?

No changes to the vibration when I go btw 2wd/4wd.

I did notice however, that at various times the lights on the dash panel for the 4wd buttons are not lighting up and when they are not lit I am unable to transfer btw 2wd/4wd. When they are lit I have no problems with the transfer. Could this be the underlying issue re the vibrations (4wd components) or just a bad electronic switch?

Also, I have noticed a periodic rough start recently that resolves itself in 20-30 seconds. Could the vibrations at 50-65mph be due to bad timing/plugs/wires? It is well overdue for a tuneup. Thanks for the help...

If a engine shake or miss.
A good tune up help.
But a tire vibration at 55-65 points to tire balance or bent wheel.

What does it do at 70 MPH or a little over?
Does it shake any more on a pull or a big hill?
Does it do it in 3 and 0D the same?

With the help of my brother in law, I finally had time to get it up on jackstands and listen to it at different speeds the noise definately originated at the rear driveshaft/u-joint. The vibration was worse at the 55-65 mph range and a metallic noise had begun especially at change of speeds. Long story short, the rear shaft u-joint at the rearend had some play and after it was removed was found to have no bearings left in one of the rollers only metal dust. We decided to replace both U-joints since they were original (149K) on the rear shaft while it was off. Great how-to on the forum btw. Heat it, hit it and replace it...Thanks for the advice and input

You are welcome and thanks for posting back how it went and the repair.
Good Luck